Can the standard Ruby logger be configured to flush after every message?

Question

Is it possible for the standard Ruby logger (i.e. ::Logger) to auto-flush after each write?

Update: I am setting a custom log formatter, as per How to get timestamps in your ruby on rails logs:

class Foo
  def initialize(params = {})
    @logger = Logger.new $stdout
    @logger.formatter = LogFormatter.new
    @logger.level = params.include?(:log) ? params[:log] : Logger::INFO
    # ...
  end

  class LogFormatter < Logger::Formatter
    def call(severity, time, progname, message)
      timestamp = time.iso8601
      log_msg = "#{timestamp}#{" [#{severity}]" if %w{ERROR WARN}.include? severity} "
      if message.is_a? Exception
        log_msg += "#{message.message}"
        log_msg += ": #{message.backtrace.join "\n#{timestamp}  "}" unless message.backtrace.blank?
      else
        log_msg += message
      end

      "#{log_msg}\n"
    end
  end
end

I tried to use the suggestion from idlefingers as follows:

  def initialize(params = {})
    Rails.logger.auto_flushing = 1
    @logger = Logger.new $stdout
    @logger.formatter = LogFormatter.new
    @logger.level = params.include?(:log) ? params[:log] : Logger::INFO
  end

But no dice. Neither does @logger.auto_flushing = 1 work for me. What am I doing wrong?

Update: It turns out that ActiveSupport's ::Logger simply wraps the standard Ruby ::Logger. So my question turns out to be about Ruby and not Rails, after all.

Answer 1

Turns out it was just a matter of turning on the sync attribute of the underlying IO object:

  def initialize(params = {})
    $stdout.sync = true unless RAILS_ENV == 'production'
    @logger = Logger.new $stdout
    @logger.formatter = LogFormatter.new
    @logger.level = params.include?(:log) ? params[:log] : Logger::INFO
  end